Internal stress wave measurements in solids subjected to lithotripter pulses

Semiconductor strain gauges were used to measure the internal strain along the axes of spherical and disk plaster specimens when subjected to lithotripter shock pulses. The pulses were produced by one of two lithotripters. The first source generates spherically diverging shock waves of peak pressure approximately 1 MPa at the surface of the specimen. For this source, the incident and first reflected pressure (P) waves in both sphere and disk specimens were identified. In addition, waves reflected by the disk circumference were found to contribute significantly to the strain fields along the disk axis. Experimental results compared favorably to a ray theory analysis of a spherically diverging shock wave striking either concretion. For the sphere, pressure contours for the incident P wave and caustic lines were determined theoretically for an incident spherical shock wave. These caustic lines indicate the location of the highest stresses within the sphere and therefore the areas where damage may occur. Results were also presented for a second source that uses an ellipsoidal reflector to generate a 30-MPa focused shock wave, more closely approximating the wave fields of a clinical extracorporeal lithotripter

An interferometric technique for B/A measurement

An isentropic phase method is described for measuringin vitro the acoustic nonlinearity parameterB/A of several aqueous buffers, protein solutions, lipid oils, and emulsions. The technique relies upon the use of an acoustic interferometer to measure the small changes in sound speed that accompany a rapid hydrostaticpressure change of between one and two atmospheres. Average accuracies of 0.85% are attainable with this method

Measurement of pressure and assessment of cavitation for a 22.5-kHz intra-arterial angioplasty device

This study was performed to understand better the mechanisms of action of an (22.5 kHz) ultrasonic wire catheter device used to remove atheromatous plaque in diseased blood vessels (ultrasonic angioplasty). During a clinical procedure, the wire acts as an acoustic waveguide to transfer acoustic energy from a generator outside the body to the ball tip of the wire, which is inserted in the blood vessel. The acoustic field radiated by the vibrating ball tip (1.5- to 3.0-mm diameter), was mapped in a relatively large (600 L) water tank and compared to the field from a well-characterized simple source. A dipolelike radiation pattern due to the translating ball tip was observed. At low power settings, standing wave effects in a smaller cylindrical volume (200-mm diameter, 350-mm height), which was used to simulate anthropometric dimensions, increase relative to the larger tank measurements. The standing wave ratio is dependent upon the pc characteristics of the medium and the dimensions of the volume, rather than on the absorption at this frequency. At high power-settings of the device, cavitation at the tip of the wire was measured using a 20-MHz passive cavitation detection scheme

Acoustical Society Of America Helmholtz-Rayleigh Interdisciplinary Silver Medal In Physical Acoustics, Biomedical Acoustics, And Engineering Acoustics: Armen Sarvazyan

The Silver Medal is presented to individuals, without age limitation, for contributions to the advancement of science, engineering, or human welfare through the application of acoustic principles, or through research accomplishment in acoustics

Evaluation of lighting conditions in portable classrooms and analysis for alternative daylighting systems

Lighting conditions in multiple classrooms in central Texas were assessed, and the feasibility of improving portable classroom daylighting via alternative daylighting systems was also evaluated. Results indicate that surveyed portable classrooms generally provide sufficient levels of light with artificial lighting systems, but have less uniform lighting distribution than permanent classrooms. To evaluate the daylight availability in portable classrooms, a model was developed and verified using field data. Climate-based daylighting simulation was performed using DIVA for Rhino, which uses Radiance and DAYSIM as simulation engines. Results from the annual daylighting analysis suggest that limited amounts of daylight were available in portable classrooms over the course of a year. In order to assess the feasibility of improving portable classroom daylighting conditions, parametric studies were completed to investigate how different factors affect the levels of light in classrooms. Simulation results suggest that increasing window area and higher window placement allow more light into the classroom. Different external shading systems also affect the indoor daylight level. However, the impact of other factors, including building orientation, ceiling-to-floor height, and classroom length-to-width ratio is minimal. While changing the window systems for an existing portable building can require a large construction effort and financial commitment, retrofitting with tubular skylights is a more approachable option. Daylighting analysis shows eight 356-mm (14-inch) diameter tubular skylights can provide the portable classroom with a sufficient light level for more than 60% of occupied hours. When daylighting alone cannot provide sufficient light, lighting control will successfully combine a daylighting system and an artificial lighting system to provide an adequate lighting environment.Civil, Architectural, and Environmental Engineerin

Bacterial Stress Responses To 1-Megahertz Pulsed Ultrasound In The Presence Of Microbubbles

Members of a panel of stress-responsive biosensors have been used to study the effect of megahertz frequency ultrasound onEscherichia coli. Insonification causes acoustic cavitation, the collapse of oscillating microbubbles in solution, which can damage bacterial cells. A focused 1-MHz ultrasound transducer, capable of generating a spatial peak pulse average intensity of 500 W/cm2, was used to treat liquid bacterial cultures. Stress-responsive promoters fused to luxCDABE allowed the continuous measurement of light produced as a result of protein damage, DNA damage, oxidative stress, and membrane perturbation. A promoter responsive to ammonia limitation was not transcriptionally activated under test conditions. In contrast to bacteria in exponentially growing cultures, those in stationary-phase cultures were more resistant to the effects of ultrasound treatment. Quantification of the degree of acoustic cavitation due to symmetric bubble collapse was measured by a 20-MHz passive transducer, the output of which appears to be only partially correlated with cellular damage and survival. The methods and results summarized here provide the basis for further investigation into applications, including the purification of water samples